The present invention relates to a device for three-dimensional investigation of an object according to the preamble of claim 1.
A device of this kind is known from DE 40 35 799. In that patent, an illuminating grid with a pixel size is imaged on a receiver array, which matches the pixel size of the photosensitive areas of the receiver array or is a whole-number multiple of said array. The diaphragm action of the receiver array is utilized. A system of this kind has the disadvantage that during the evaluation of images taken from various focal planes to determine the depth values, the absolute brightness values are always evaluated and their maximum must be determined.
A device is known from JP 1-55513(Feb. 3, 1989) which is suitable for rapidly focusing a microscope using incident light from the aid of a laser beam. For this purpose, a photodiode is utilized with four receiver segments and the object point illuminated by the laser is imaged through an optical system with cylindrical lenses on the four-quadrant receiver. This principle differs however basically in its effect from pupil division, since no focused image of the object point is produced. The device according to JP 1-55513 is unsuitable for rapid 3-D measurement.
DD 265 224 likewise describes a device with point-wise object illumination, but it only makes it possible to measure an object location simultaneously. It is likewise unsuited for rapid measurement of large sample areas.
DE 26 34 655 teaches a device for focusing a single-lens reflex camera. It is unsuited for measuring 3-D objects.
In the book "Technische Optik" [Technical Optics] by Gottfried Schroeder, Vogel-Verlag, 1977, page 145, a device from the field of photography is described that uses a double prism and serves to focus a camera. Since only one object position is detected, this system cannot be used for automatic measurement of larger object areas.
A device that makes it possible to determine the focus of an individual measurement point with a zero signal detection is known from the company publication "Microfokus, Beruehrungslos messen" [Microfocus, Measurement with Zero Contact] from UBM Messtechnik, D 76275 Ettlingen. In that publication, the light from a laser diode is imaged on the object to be illuminated and the light reflected from this object is split by a pair of prisms so that the two half pupils are imaged on two receiver pairs. The light from a laser diode is imaged on the object to be measured and the light reflected from the object is split by the pair of prisms in such fashion that two half pupils are imaged on two receiver pairs*. A system of this kind, apart from the focus, supplies a directional signal that indicates the direction in which the position of the measured object differs from the focus position. However, only a single point on the object is detected. Measurements with a system of this kind therefore require a great deal of time, especially when large areas of the object are to be measured.
 FNT *Evident repetition. Translator's note.